Abstract
Experiments were performed with two circular cylinders whose walls were porous and permeable in order to investigate the effects of flow of water through the wall. Each cylinder was made of bronze sintered compact, available as a sintered metallic filter. It had an outside diameter of 30 mm, a wall thickness of 2 mm and a nominal filter size of 2 μm or 20 μm. Force coefficients and pressure distributions of the test cylinders were measured over the Reynolds number range of 1.1×105∼4.4×105 and were compared with those of the same porous cylinders into which another circular cylinder, an "inner cylinder" with a solid wall, was inserted to obstruct such a through-flow. The measured results showed that the drag coefficients and the root-mean-square values of the fluctuating lift coefficients of the test cylinder equipped with the inner cylinder were smaller than those with the through-flow. This was caused by the increase in the effective surface roughness and the altered pressure distribution because of the permeability of the cylinder wall. The increase in the drag coefficient was accompanied by the decrease in the Strouhal number of the fluctuating lift, and vice versa.
